Armature set up - some problems rigging a spider


I have a few questions about rigging a model of a spider. I can do basic rigs that I’d like to improve and there are a couple of things that bug me about my existing rigs.

  1. Is there a way to rig a mesh like this so that it behaves like a hard surface rig? What I mean is that the segments of the spider should remain non-flexible, and the flexible part is the membrane between joints. With the automatic bone weights method, there is always some flex and distortion of the segments, even with weight painting set to 0 for these areas. Is there a way to parent segments to bones without them being separate objects?

Another example of the problem, here the spine is being deformed when the fang is moved. There isn’t any weight on the teeth from these bones but they are still being affected.

  1. I have the legs set up to be controlled with IK chains, and these seem to work fine. I then parented each leg to a bone in the cephalothorax (head), so that if the body was tilted, the legs would not cause the mesh to deform. However, I now have a problem that the IK chains all seem to affect each other now. If I move a leg for example, it will cause the cephalothorax to also tilt that direction. Likewise, if I tilt the cephalothorax up, it seems like the last segment of the legs and palps are stuck in their original positions (it’s clearer in the photos).

Don’t know if this will help you or not. But on your topology, the spillover on weights will “pull” and “collapse” other vertices with it. So you can look at some examples for getting crisp deformations to correct that with better topology. to start with.

On your weight painting it is really hard to tell what you have. But here is an oldy but goodie that I think will help you see what you are looking at. Since I don’t have your blend file I can’t be sure, but I’m betting your just not seeing the weights.

So to answer your questions, I would think about redoing the topology on your joints to start with. Secondarily, I would fine tune your weight painting.

I hope this helps.

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Vertices with different weights will deform. Vertices with the same weights will stay a solid piece. Probably the best thing to do is to select a bit you want to remain solid, actively select a bit in the center of that selection, and use sidebar/item/vertex weights/copy to copy from actively selected vert to all selected verts.

Regarding your IK, I would check your chain lengths. From the looks of your legs, your chain lengths may be 5, but shouldn’t be longer than that. 0 chain length means it affects everything; 0 is really infinity.

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I just realised I had the wrong bone selected so that is indeed nonsensical! But that video is very interesting. I’m curious as to how it would work for joints that can bend in two directions.

Good tip, will try that. I can always tell it’s the end of the day when I hit these issues, I end up missing the lateral thinking approaches!

I was stuck on this for ages, then figured out a solution with the weight paints which I think works well for these sorts of legs. It seems faster than trying to copy vertex groups from one mesh to another (not sure if there are other ways). Although I think this might be one of those times where anyone who actually rigs properly is like “duh, how else would you do it” :smiley:

  1. Do the usual armature parenting with automatic weights

  2. For each bone weight group, select the segment (I do this via UV islands). Assign this with weight 1.

  3. Select the segments either side of your “focal segment” - then remove these from the weight group.

e.g. in the photo the trochanter is the focal segment (red) and the coxa and femur are removed.

This gives a nice sharp segment and keeps the “smoothing” between so that the integument bends without too many issues.

I didn’t recommend copying from one mesh to another-- you’re copying from a vertex to surrounding vertices. However, assignment works too, if you’re happy with the weights you’re getting from it.

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Ah sorry, I realise I wrote that a little unclear - what I meant was that in searching for more info on your suggestion, all I could find were tutorials copying vertex groups from one mesh to another.